Tiny pieces of plastic and man-made fibres are causing contamination of the world's oceans and beaches, the journal Science has reported.

Even remote and apparently pristine layers of sand and mud are now composed partly of this microscopic rubbish, broken down from discarded waste.

This is the first assessment of plastic fragments accumulating in sediments and in the water column itself.

It is not yet known what the long term effects of this pollution may be.

A team led by scientists at the universities of Plymouth and Southampton took samples from 17 beaches and estuaries around the UK, and analysed particles which did not appear to be natural.

The researchers found that most samples included evidence of a range of plastics or polymers including nylon, polyester and acrylic.

It suggests to us that the problem is really quite ubiquitous

Dr Richard Thompson, University of Plymouth

They also found that when creatures such as lugworms and barnacles fed on the sediments, the plastics turned up inside their bodies within a few days.

To test whether this contamination was getting worse, the scientists analysed plankton samples taken from survey ships between Scotland and Iceland since the 1960s - and found that the plastic content had increased significantly over time.

Toxic chemicals

Because the team only sampled particles which looked different from natural sediments, it is believed that the true level of plastic contamination could be much higher.

The lead author of the study, Dr Richard Thompson, said: "Given the durability of plastics and the disposable nature of many plastic items, this type of contamination is likely to increase.

This rocket casing is one of the more unusual pieces of litter on the world's beaches

"Our team is now working to identify the possible environmental consequences of this new form of contamination."

One concern is that toxic chemicals could attach themselves to the particles which would then help to spread them up the food chain.

That research is for the future, but this study suggests that practically everything really is made of plastic these days - even the oceans.

"We've found this microscopic plastic material at all of the sites we've examined," Dr Thompson said.

"Interestingly, the abundance is reasonably consistent. So, it suggests to us that the problem is really quite ubiquitous."